-er bbb bbc bbe bbk bbn bbo bbr bcb bcc bce bck bcn bco bcr be- beb bec bee bek ben beo ber bkb bkc bke bkk bkn bko bkr bnb bnc bne bnk bnn bno bnr bob boc boe bok bon boo bor brb bre brk brn bro brr c-- cbb cbc cbe cbk cbn cbo cbr ccb ccc cce cck ccn cco ccr ce- ceb cec cee cek cen ceo cer ckb ckc cko cn- cnb cnc cne cnn cno cnr co- cob coc coe cok con coo cor crb crc cre crk crn cro crr ebb ebc ebe ebk ebn ebo ebr ec- ecb ecc ece eck ecn eco ecr eeb eec eee eek een eeo eer ekb ekc eke eko ekr en- enb enc ene enk enn eno enr eo- eob eoc eoe eok eon eoo eor erb erc ere erk ern ero err kbb kbc kbe kbk kbn kbo kbr kcb kcc kce kck kcn kcr ke- keb kec kee kek ken keo ker kkb kkc kke kkk kkn kkr kn- knc kne knk knn kno knr kob koc koe kok kon koo kor krc krk krn kro krr nbb nbc nbe nbk nbn nbo nbr ncb ncc nce nck ncn nco ncr ne- neb nec nee nek nen neo ner nkc nke nkk nkn nko nkr nnb nnc nne nnk nnn nno no- nob noc noe nok non noo nor nrb nrc nre nrk nrn nro nrr ob- obb obc obe obk obn obo obr oc- ocb occ ock ocn oco ocr oeb oec oee oen oeo oer okb okc oke okk oko okr on- onb onc one onk onn ono onr oo- oob ooc ook oon ooo oor or- orb orc ore ork orn oro orr rbb rbc rbe rbk rbn rbo rbr rcb rcc rce rcn rco rcr re- reb rec ree rek ren reo rer rkb rkc rke rkk rko rnb rnc rnn rno rnr rob roc roe rok ron roo ror rrb rrc rrk rrn rrr